Actually there are combos that work against lore or that can't work:
-undead druids - really being sort of dead and trying to bring life is something of a contradiction, the nature magic would effectively destroy the undead for real if used due to how it works. This is not like the Light where an undead could channel it with great pain, nature and undeath are in pure contradiction as there is nothing natural about the state of undeath
-draenei warlocks - when draenei left the erredar they did so because they desired to have nothing to do with fel. Having draenei warlocks would mean they are the erredar.
-goblin druid - goblins desire wealth above all and stop at nothing to achieve it, destroying nature wherever they go. They could not control nature at any point ever for, while it would not kill them per say, it would mean abandoning everything their race is about.
-gnome shaman - last but not least, gnomes are quite destructive to the land itself too. While at least one in Blade's Edge was trying to learn more about how druidism works, and it could work (just like asura in Guild Wars 2 who have towns wonders of tech but intertwined with nature), they constantly have to battle the elements but, unlike goblins, would not subjugate them to their will, meaning they will be in constant contradiction with them.
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Here's the deal, the worgen harvest witches also only knew the botanist aspects so to say before night elves helped them understand the rest.
Furthermore, yes, blood elves use arcane to bend magic to their will. In a way, their view on druidism is similar to the taunka view of shamanism. While tauren/orcs/trolls believe they need to ask the elements for aid and offer them stuff, the taunka force the elements to their will through their power. Same here, while the rest of the druids are in tune with nature, blood elves would force nature to bend to their will through arcane. They would probably never be allowed in Moonglade lorewise, but they could be druids per say.
Also, draenei seem to have been trying to learn about druidism since their starting zones and now in WoD we saw draenei who try to blend in with nature. Overall, best candidate.